Guidance, navigation, pointing and tracking systems use gyroscopes, accelerometers, and various other sensors to obtain highly accurate data. A gyroscope, for example, uses a spinning mass to sense rotation rates. One type of gyro is the rate integrating type which balances the input rate against a torque exerted by a current carrying coil in the presence of a magnetic field. The current can be scaled to produce the desired counter-torque, and measured to indicate the input rate, or integrated and measured to indicate the input change in angle.
Servo loops used in such sensor applications have some degree of temperature sensitivity. This sensitivity can be a serious problem depending upon the type of loop designed and the accuracy required. For example, in a rate integrating gyro application, as the current is varied to match the input rate, the thermal effects resulting from this current change produce errors in the data such as scale factor drift and bias drift. Existing ways of dealing with such problems are directed at precise temperature regulation of the servo loop environment. In the rate integrating gyro or any other such device it would therefore be desirable to supply constant power to the device's torquer regardless of the input rate. Existing designs switch the direction of constant current through a torquer to achieve constant power, e.g., a variable duty cycle scheme whereby the current is maintained constant by switching its direction through the torquer coil and modulating its duration, to control the net torque in a desired direction. This approach provides the desired constant power but introduces some effects that could compromise performance for low noise applications. This is due to the bidirectional pulse width modulating technique which introduces noise at harmonics of the modulating frequency.